Semiconductor devices, to be useful, must be electrically connected to one another or to other electronic devices. Leadframes made from conductive metal such as copper, silver or gold are often used to electrically connect a semiconductor device to other electronic devices. One popular and flexible method of connecting semiconductor devices to leadframes is wire bonding. Bond wires usually consist of aluminum, copper or gold. Bond wire diameters typically range from about 15 μm to several hundred micrometers in high-power applications. There are two basic types of wire bonding—ball bonding and wedge bonding.
In ball bonding, a small molten ball is formed at the end of the bond wire by application of a high voltage charge through a tool known as a capillary that holds and dispenses wire. The molten ball is placed on the electrical contact surface of a chip. The contact surface is usually copper or aluminum. A combination of heat, pressure and ultrasonic energy is then applied, which creates a weld between the ball and the contact surface. The ball bond is sometimes referred to as the first bond because it is usually the first bond made in wire bonding of an IC chip/die to a leadframe.
In a die leadframe interconnection, the type of wire bond that is generally used to connect the second end of the bond wire to the leadframe is called a wedge bond or sometimes a second bond. It is formed by crushing the end of the bond wire between the leadframe or other metal surface and the tip of the capillary tool.
The quality of wire bonds formed on a leadframe is dependent on a number of factors including the stability of the leadframe on a support plate of the bonding machine.